Multi-layered wound dressing

ABSTRACT

A multi layered wound dressing which comprises an adhesive layer, an absorbent layer overlying said adhesive layer on the surface furthest from the wound, and a moisture transmitting cover layer overlying the absorbent layer, the dressing having a total thickness of less than 1.5 mm.

[0001] This application claims the benefit of priority of United KingdomPatent Application No. GB 0017080.3, filed on Jul. 12, 2000, the entirecontents of which are herein incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a multi layered wound dressingparticularly, but not exclusively, for use as a dressing on highlyexuding wounds located on areas of the body that require a high degreeof flexibility from the dressing.

BACKGROUND OF THE INVENTION

[0003] It is known to make wound dressings for use on heavily exudingwounds from materials with a high moisture vapour transmission rate(MVTR). Such dressings rely on exudate being taken up by the dressingand spread across much of the surface area of the dressing in order toensure sufficient moisture evaporation. Examples of such dressings areALLEVYN™ marketed in adhesive or non-adhesive versions by Smith andNephew or TIELLE™ marketed by Johnson and Johnson. Such dressings arenot designed to absorb and retain the exudate but manage the exudate byallowing the moisture present in the exudate to evaporate. Adisadvantage of such dressings is that the lateral wicking of exudate isnot contained and can cause normal skin surrounding the wound tomacerate. A further disadvantage of such dressings is that the rapidloss of exudate can cause the wound to desiccate.

[0004] It is also known to make wound dressings for use on heavilyexuding wounds from absorbent materials that absorb and retain exudatein the dressing. A disadvantage of such dressings is that they tend tobe rather thick and not particularly conformable to those wounds locatedin areas requiring a high degree of flexibility from the dressing suchas elbows and heels.

[0005] There is thus a need for a wound dressing which is capable ofmanaging exudate at the rate it is produced by a wound and which also isable to conform to wound sites on highly contoured areas of the bodysuch as elbows and heels.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a multi layered wounddressing. The dressing comprises an adhesive layer, an absorbent layeroverlying the adhesive layer on the surface furthest from the wound, anda moisture transmitting cover layer overlying the absorbent layer. Thedressing should have a total thickness of less than 1.5 mm. In oneembodiment, the cover layer has a moisture vapour transmission rate ofat least 500 mg2. In some embodiments, the adhesive layer is aperturedand/or can comprise a mixture of hydrocolloids and polyisobutylene. Insome embodiments, the absorbent layer can be of a carboxymethylatedfabric.

[0007] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary, butare not restrictive of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0008] We have now invented a multi layered wound dressing whichalleviates the above problems by combining absorption and moisturetransmission in a conformable format and there is provided by a firstembodiment of the present invention a multi layered wound dressingcomprising:

[0009] (1) an adhesive layer,

[0010] (2) an absorbent layer overlying said adhesive layer on thesurface furthest from the wound, and

[0011] (3) a moisture transmitting cover layer overlying the absorbentlayer, the dressing having a total thickness of less than 1.5 mm.

[0012] Preferably the total thickness of the dressing is between 0.3 to1.5 mm, more preferably between 0.4 to 1.0 mm and most preferablybetween 0.5 to 0.8 mm.

[0013] Preferably the dressing has a fluid handling capacity of at least2 g/10 cm2/24 hr, more preferably between 2 g/10 cm2/24 hr and 20 g/10cm2/24 hr and most preferably between 4 g/10cm2/24 hr and 15 g/10 cm2/24hr. We have found that wound dressings according to the invention maymitigate the problems associated with the management of high levels ofexudate produced by some wounds yet be readily conformable to highlycontoured wound sites and not lead to desiccation of the wound. It isthought that this is in part achieved by the selection of the absorbentlayer which provides absorbency and acts as a reservoir of moisture todeter wound desiccation, without adding to the bulk of the dressing.This allows the manufacture of a thin dressing which has the fluidhandling capacity of a much thicker dressing.

[0014] Preferably the cover layer has a high MVTR. This allows moistureto evaporate from the dressing and in combination with the absorbentlayer assists in the reduction of bulk in the dressing.

[0015] The cover layer of the present invention is preferably a layerhaving a MVTR of at least 3000 g/m²/24 hr measured by the methoddescribed in 1993 BP Appendix XX J1 in or in the range of from 1000g/m²/24 hr to 10000 g/m²/24 hr. The cover layer may be in the form offilm or a film/foam laminate. Examples of film materials which may beused as cover layers include polyurethanes; polyureas; homo- andcopolymers of vinyl acetate; polyethers; polymers comprising amideblocks; homo- and copolyesters; or a combination of two or more ofthese. A film/foam laminate which may be used as cover layer of a wounddressing of the invention is an expanded polyurethane foam laminated toa polyurethane film.

[0016] The absorbent layer is present to absorb exudate from the woundand provide a reservoir of moisture to deter wound desiccation. Thelayer preferably has an absorbency of at least 10 g/g sodium/calciumchloride solution BP, more preferably from 12 to 26 g/g and mostpreferably an absorbency of from 14 to 20 g/g. The absorbent layer ispreferably fibrous and most preferably comprises gel forming fibres. Theabsorbent layer preferably has a thickness from 0.2 to 1.4 mm, morepreferably from 0.35 to 0.95 mm and most preferably 0.4 to 0.65 mm.

[0017] The gel forming fibres are preferably chemically modifiedcellulosic fibres in the form of a fabric and in particularcarboxymethylated cellulose fabrics as described in WO 00/01425 to AkzoNobel UK Ltd. The carboxymethylated cellulosic fabrics preferably have adegree of substitution of between 0.12 and 0.35 as measured by IRspectroscopy and are made by carboxymethylating a woven or non-wovencellulose fabric such that the absorbency is increased.

[0018] The cellulosic fabric preferably consists solely of cellulosicfibre but may contain a proportion of non-cellulosic fibre but maycontain a proportion of non-cellulosic textile fibre or of gel-formingfibre. The cellulosic fibre is of known kind and may comprise continuousfilament yarn and/or staple fibre. The carboxymethylation is generallyperformed by contacting the fabric with strong alkali and acarboxymethylating agent such as chloroacetic acid in an aqueous system.

[0019] Another suitable gel forming fibre comprises alginate fibre.Alginate fibres may be used alone in the absorbent layer or in admixturewith non-cellulosic textile fibre, with other gel-forming fibre such ascarboxymethyl cellulose fibre, or with both. A particularly preferredsuch fibre is an absorbent, composite fibre comprising a matrix of fromat least 10% to less than 50% by weight of water insoluble alginate,such as calcium alginate, having dispersed therein at least 40% byweight or another polysaccharide. Suitably, the other polysaccharide maybe selected from the group comprising carboxymethyl cellulose,carboxyethyl cellulose, other derivatives of cellulose, cellulose,pectin, hyaluronic acid and chitosan.

[0020] A method for making such absorbent, composite fibres comprisesthe following steps:

[0021] i) adding sodium alginate and another polysaccharide to water toform a dope;

[0022] ii) forcing the dope through a spinneret to form fibres;

[0023] iii) treating the resulting fibres with a source of ions toconvert the alginate to water insoluble alginate and cross-link thealginate to the other polysaccharide;

[0024] iv) drying the fibres.

[0025] The adhesive layer of the present invention forms the woundcontacting surface of the dressing and adheres the dressing to the skin.Preferably the adhesive composition comprises a homogenous blend of oneor more water soluble hydrocolloids and one or more low molecular weightpolyisobutylenes such as are described in EP-B-92999 incorporated hereinby reference. The water soluble hydrocolloids may be selected fromsodium carboxymethylcellulose, pectin, gelatin, guar gum, locust beangum, gum karaya, and mixtures thereof. The polyisobutylenes may beselected from low molecular weight polyisobutylenes having a viscosityaverage molecular weight of from 36,000 to 58,000 (Florey). The adhesivelayer is capable of absorbing exudate while maintaining adhesion of thedressing to the skin.

[0026] Alternatively the adhesive composition may comprise a homgeneousblend of one or more hydrocolloids, one or more low molecular weightpolyisobutylenes, one or more styrene block copolymers, mineral oil,butyl rubber, a tackifier and small amounts of optional components. Byselection of specific ranges of the amounts of the above listedcomponents, adhesive compositions may be prepared having good adhesionto the skin and stretchability. Such compositions and the preparationthereof are disclosed in EP-B-130061 incorporated herein by reference.

[0027] The adhesive composition may also comprise reinforcing fibressuch as described in EP-B-130061 and EP-A-621042 to aid in themaintenance of the structural integrity of the dressing. Preferably thereinforcing fibres are present at a level of from 2% to 10% by weight ofthe adhesive composition. The adhesive layer may be substantially freefrom apertures; alternatively, it may include a plurality, preferably asa regular array, of apertures from 0.25 to 10 mm in diameter, especiallyfrom 5 to 8 mm in diameter.

[0028] The composition may be in form of a layer of the island typewhere different regions of the adhesive layer have different properties.For example the adhesive layer could comprise a central zone ofswellable material backed and surrounded by a more rigid adhesive or theadhesive layer could be apertured to allow rapid uptake of exudate intothe dressing.

[0029] The dressing will typically be made in three sizes, 55 mm×55 mmsquare, 105×105 mm square and 205×105 mm rectangular, all dressingspreferably being about 0.6 mm thick.

[0030] Preferred embodiments of the invention will now be illustrated inthe following examples.

EXAMPLE 1

[0031] A multi layered dressing according to the invention was made byobtaining an absorbent layer as described in WO 00/01425 having a lowdegree of substitution and in the form of a hydroentangled aperturedfabric and bonding it to a polyurethane film coated with an adhesive byconventional heat lamination/pressure techniques.

[0032] An adhesive is applied by extrusion in the correct dimensionsonto silicone release paper and then transferred onto the absorbentlayer of the dressing, either prior to or subsequent to the heat sealingprocess. In this way the adhesive is keyed into the absorbent layer viaconventional pressure/heat lamination techniques. The dressings werepress cut or roller cut from the laminated web.

EXAMPLE 2

[0033] The fluid handling characteristics of various embodiments of thepresent invention were compared to a commercially available thindressing. Total Dressing Moisture vapour Fluid Absorbed Fluid handlingDressing Thickness (mm) Transmission (g) (g) Capacity (g) Example 1 withApprox 2.47 2.03 4.50 fabric absorbent 0.5-0.6 layer omitted Example 1with 0.55 3.60 1.78 5.38 fabric absorbent layer omitted and aperturedadhesive Example 1 0.79 2.05 2.25 4.30 Example 1 with 0.84 5.62 2.418.03 apertured adhesive DuoDERM 0.66 0.23 1.26 1.49 Extra Thin

[0034] Moisture vapour transmission, fluid absorbed and total fluidhandling are measured as per BP, 1996, monograph for hydrocolloiddressings, fluid handling test.

EXAMPLE 3

[0035] A multi layered dressing was made as follows: the absorbent layerwas placed onto a flat surface and coated with about 10 to 20 gms ofco-polyamide powder bond material. The polyurethane film material (plusits support) was then placed onto this and the assembly passed through afusing press at about 100 □C.

[0036] A sheet of hydrocolloid adhesive with 5 mm perforations was nextplaced onto the absorbent surface of the assembly and bonded (on thefusing press set at 80 □C). As previously explained in Example 1 theadhesive is now keyed-in to the dressing.

[0037] A fresh piece of release liner was placed across the hydrocolloidlayer and the final dressing shape was cut out. The dressings were thenpackaged and irradiated at 35.5 kGy prior to testing.

[0038] Thickness determination of extra thin dressings with varyingfilms applied. Sample Thickness (mm) Std. Dev. Sample 10.64 0.07 Sample20.65 0.07 Sample 30.78 0.05

1-9. Canceled.
 10. A multi layered wound dressing which comprises: an adhesive layer, an absorbent layer overlying said adhesive layer on the surface of the adhesive layer furthest from the wound, and a moisture transmitting cover layer overlying the absorbent layer, wherein the dressing has a total thickness of less than 1.5 mm and wherein the dressing exhibits a fluid handling capacity of at least 2 g/10 cm²/24 hr.
 11. The multi layered wound dressing of claim 10 wherein the adhesive layer is apertured.
 12. The multi layered wound dressing of claim 10 wherein the adhesive layer comprises a mixture of hydrocolloids and polyisobutylene.
 13. The multi layered wound dressing of claim 10 wherein the absorbent layer is a carboxymethylated cellulosic fabric.
 14. The multi layered wound dressing of claim 10 wherein the absorbent layer is from 0.2 to 1.4 mm in thickness.
 15. The multi layered wound dressing of claim 10 wherein the absorbent layer is from 0.4 to 0.65 mm thickness.
 16. The multi layered wound dressing of claim 10 wherein the cover layer has a moisture vapour transmission rate of at least 500 g/m²/24 hr.
 17. The multi layered wound dressing of claim 10 wherein the dressing exhibits a fluid handling capacity of between 2 g/10 cm²/24 hr and 20g/10 cm²/24 hr.
 18. The multi layered wound dressing of claim 10 wherein the dressing exhibits a fluid handling capacity of between 4 g/10 cm²/24 hr and 15 g/10 cm²/24 hr.
 19. The multi layered wound dressing of claim 10 wherein the absorbent layer exhibits an absorbency of at least 10 g/g sodium/calcium chloride solution BP.
 20. The multi layered wound dressing of claim 10 wherein the absorbent layer exhibits an absorbency of 12 to 26 g/g sodium/calcium chloride solution BP.
 21. The multi layered wound dressing of claim 10 wherein the absorbent layer exhibits an absorbency of 14 to 20 g/g sodium/calcium chloride solution BP.
 22. A multi layered wound dressing which comprises: an adhesive layer, an absorbent layer overlying said adhesive layer on the surface of the adhesive layer furthest from the wound, wherein the absorbent layer is fibrous; and a moisture transmitting cover layer overlying the absorbent layer; wherein the dressing has a total thickness of less than 1.5 mm.
 23. The multi layered wound dressing of claim 22 wherein the adhesive layer is apertured.
 24. The multi layered wound dressing of claim 22 wherein the adhesive layer comprises a mixture of hydrocolloids and polyisobutylene.
 25. The multi layered wound dressing of claim 22 wherein the absorbent layer is a carboxymethylated cellulosic fabric.
 26. The multi layered wound dressing of claim 22 wherein the absorbent layer is from 0.2 to 1.4 mm in thickness.
 27. The multi layered wound dressing of claim 22 wherein the absorbent layer is from 0.4 to 0.65 mm in thickness.
 28. The multi layered wound dressing of claim 22 wherein the cover layer has a moisture vapour transmission rate of at least 500 g/m²/24 hr.
 29. The multi layered wound dressing of claim 22 wherein the dressing exhibits a fluid handling capacity of between 2 g/10 cm²/24 hr and 20g/10 cm²/24 hr.
 30. The multi layered wound dressing of claim 22 wherein the dressing exhibits a fluid handling capacity of between 4 g/10 cm²/24 hr and 15g/10 cm²/24 hr.
 31. The multi layered wound dressing of claim 22 wherein the absorbent layer exhibits an absorbency of at least 10 g/g sodium/calcium chloride solution BP.
 32. The multi layered wound dressing of claim 22 wherein the absorbent layer exhibits an absorbency of 12 to 26 g/g sodium/calcium chloride solution BP.
 33. The multi layered wound dressing of claim 22 wherein the absorbent layer exhibits an absorbency of 14 to 20 g/g sodium/calcium chloride solution BP. 